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2.2. Programming and reading ETM9 registers

All registers in the ETM9 are programmed through a JTAG interface. The interface is an extension of the ARM TAP controller, and is assigned scan chain 6.

The scan chain consists of a 40-bit shift register comprising:

  • a 32-bit data field

  • a 7-bit address field

  • a read/write bit.

The general arrangement of the ETM9 JTAG registers is shown in Figure 2.1.

The data to be written is scanned into the 32-bit data field, the address of the register into the 7-bit address field, and a 1 into the read/write bit.

A register is read by scanning its address into the address field and a 0 into the read/write bit. The 32-bit data field is ignored.

A read or a write takes place when the TAP controller enters the UPDATE-DR state.

For further details of ETM9 registers, see the Embedded Trace Macrocell Specification.

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